Electrical conductor



April 29, 1930- 4 A0.15. BUCKLEY 1,756,341 y' ELECTRICAL CONDUCTOR FiledDec. 5l, 1924 I l l Coding of Coppver Onde Patented pr. 29, 1930 UNITEDSTATES- PATENT OFFICE OLIVER E. BUCKLEY, OF MAPLEWOOD, NEW JERSEY,ASSGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, 0F NEW YORK, N. Y., ACORPORATION OF NEW YORK ELECTRICAL CONDUCTOR Application filed December31, 1924. Serial No. 758,984.

This invention relates to conductors for the transmission of electricalenergy and more particularly to signaling conductors having an externallayer of a material of high permeability for the purpose of increasingthe inductance of the conductor.

Onemanner of increasing the inductance of the conductor employed for thetransmission of alternating current is to wrap the conductor spirallywith a layer of wire or tape of magnetic material. This method is knownin the art as continuous inductive loading as distinguished from lumploading by means of inductance coils distributed at intervals along theconductor. Until recently iron has been considered to be the onlymaterial suitable for continuous loading but it has now been discoveredthat a more suitable material may be procured in the form of an alloy ofnickel and iron. Then these two metals are combined in the properproportions and the resulting alloy is given a proper lheat treatment, amaterial having a very high permeability at low magnetizing forces isobtained. One' form of this material which has been used in a submarinecable comprises TS1/2% nickel and 2l1/2% iron. Alloys of nickel and ironhaving similar characteristics, especially high permeability at lowmagnetizing forces vhave been styled permalloy Other propertiespossessed by these alloys which increase their value as a loadingmaterial are a hysteresis loss lower than that of iro'n and a highresistivity, both properties being conducive to increasing theefticiency of the cable by lowering the effective resistance of theconductor. When it was attempted to employ this material in the form ofa tape for continuous loading, difficulties were encountered. It wasfound that if the permalloy tape was first heated and then cooled beforeapplying to the conductor, internal stresses were set up upon bending ofthe tape, causing the permeability to be very materially lowered. Thisdifficulty was overcome by applying the tape to the conductor beforegiving the tape the heat treatment and then subjecting the tapedconductor to the heating and cooling necessary to prod'ucle highpermeability in the loading materia v Further difficulty, however, wasexperienced in that the permeability of the loading material was loweredby what appeared to be adhesion between the copper conductor and theloading tape. It is believed that this adhesion occurs when the tapedconductor is sub3ected to the high temperatures necessary for the properheat treatment and thatv upon structure with very little space notoccupied by metal. To give the loading material the desired magneticcharacteristics, this conductor was heated to approximately 850 C. andthen cooled at apreferred rate. O-n heating1 both metals expand but thecopper, because of its higher temperature coefticient, expands more thanthe loading material with the result that it presses tightly against theloading material when the conductor is at the high temperature and ifthe structure is a fairly tight one, the magnetic tape is stretched, anelongation of 1% having been observed. This stretching has apparently nodirect effect on the magnetic properties since it occurs at atemperature above the magnetic transformation point but it does showeffects of high pressure between the metals.` At the temperature of 850C. both metals arc relatively soft and since they are forced together bythermal expansion there is a tendency .for the loading material to weldto the copper, the extent to which the metals are welded dependsoy ingon several factors such as the tightness of the copper' structure andthe character of the metal surfaces. In this connection it has Abeennoted that although the loading material welds to the copper, `weldingof the copper strands to the central wire has'been veryrarely observedand no welding has been observed between layers of the loa ding materialwhen more than one layer has been used. These results suggest thatWelding is possibly not a simple case of fusion of the two metals butsome effect` brought about by chemical action.

On cooling, the copper conductor contracts more than the magnetic tape.No doubt some of the welds Which have been formed break loose when thiscontraction occurs but the stronger ones hold With the result that themagnetic tape is at points pulled down with the copper and parts of itare bent, stretched or compressed depending upon the particularaccidental conditions of adherence. Even though the forces involved maybe very small, the stresses at points in the tape may be of considerablemagnitude giving strain suffi- -cient to reduce the permeability atspots to a very small fraction of that which the` tape would have had ifnot subjected `te .such strain. The resultant conductor, therefore, is.one which although it may have fairly uniform inductance as measuredfrom foot to foot 'is loaded with a material which varies inpermeability over a wide range in points separated by a fraction of aninch.

The copper strands upon being stranded about the central conductor donot present a true cylindrical surface since the edges of the strands donot lie in close contact withv the central conductor but presentspiralled edges. As the cooling proceeds, therefore a sticking orWelding of the material may occur at various points along these edgesand the subsequent contraction of the copper set up ,stresses in thealloy tape.

During the cooling portion of the heat treatment the alloy tape may coolmore rapidly at first than does the copper conductor due to its intimatecontact with the cooling medium so ,that the alloy tape quickly comesinto intimate contact with the copper strands.

Whatever may be the true explanation for the difficulty experienced, ithaslargel'y been overcome by providing a small air space between thelayer of loading mater' l and the signaling conductor when the loac ingmaterial is applied This method of obtaining high permeability isdescribed at length in patent to G. lV.Elmen, No. 1,586,887, issued onJune l, 1926. l

Instead of providing an air space between the conductor and the tape, asthe latter is Wound in position, the desired result may be obtained byplacing a layer of paper upon the conductor before .the loading materialis Wound thereon.

This layer of paper is` burned out during the subsequent heat treat-kment thus giving the desired spacing between the loading material' andthe conductor. This method is described in detail in patent to V. B. TenEyck No. 1,586,862, issued on June 1, 1926.

During the heat treatment the loaded conductor is passed through aheated tube for the market contains a certain amount of copper oxide,and when the copper conductor is heated in the presence of a reducingatmosphere, the copper oxide is dissolved, thereby rendering theconductor brittle. Various means have been. proposed for preventing thisembrittling action, such for example, as

the method disclosed in patent -to J. W..

Harris No. 1,586,897, issued on June 1, 1926.

In this method, which has been the preferred method used commerciallyheretofore, a stream of nitrogen is forced through the heating tube in adirection opposite to the direction of movement" of the conductor,thereby sweeping out the reducing gases as soon I11s-they are releasedand thus protecting l the conductor. This process, however, isexpensive,` and moreover, is objectionable because of the fact thatthere is always an element of risk involved since failure of the flow ofnitrogen might be of serious consequence.

An object of the present invention is to provide'for the practicalloading of a signaling conductorwith magnetic material which requiresheat treatment and whose characteristics are subject to undesired changeunder appliedstresses.

Another object of the invention is to provide a methodof applyingmagnetic loading material to an electrical conductor in sucha manner asto prevent the setting up of deleterious stresses in the magneticmaterial during the subsequent lieat treatment.

A further object of the invention is to subject the loaded conductor tothe desired heat treatment Without danger of embrittling the conductor.

To accomplish these objects, the invention contemplates an electricalconductor upon which is applied a loading material capable of possessinghigh permeability and the method of applying this material to theconductor in such a way as to avoid obtaining low or variable values ofpermeability. This invention is in the nature of an alternative to thosedisclosed in the above mentioned patents to G. lV. Elmen and lV. B. TenEyck. Each `of these inventions has certain advanllO tages over theothers as will be apparent from a consideration of the several patents.

The invention may be more clearly understood by reference to theaccompanying drawing in which- Fig. 1 is a view of a loaded conductor,certain portions being shown cut away to more clearly disclose thestructure;

Fig. 2 is a cross-sectional view of the conductor of Fig. 1; and

Fig. 3 is a view showing apparatps which maybe used for applying theheat treatment to the conductor.

Referring to` the drawing, the electrical conductor preferably comprisesa central core member 10 of conducting material about which a pluralityof conducting strands 11--11 are wrapped with a spiral lay. About thiscomposite conductor is wrapped the tape 12 which preferably consists ofan alloy containing 78V3% nickel and 21%270 iron. The surfaces of member10 and strands 11-11 are provided with a coating of vcopper oxide, whichpreferably is formed at the time of f annealing the individual parts ofthe composite conductor. This may be accomplished by simply exposing thecopper conducting strands to air at a suitable stage in the annealing.process instead of protecting them from air during annealing -as isordinarily done in commercial practice.

After the stranded conductor isformed of the central oxidized copperwire and the oxidized copper tape andy the composite conductor isprovided with one or more layers of permalloy tape applied sutlicientlytightly to make a good mechanical structure, the resulting conductor istreated by passing it through a heated tubular furnace of the typedisclosed in Fig, 3. This furnace which is of the muflie type-comprisesheating elements 30 which are located between the re clay muflie 31 andthe tire brick 32. The iron tube 33 has a copper lining 34 of such smallinside diameter as to prevent rapid circulation of air which would causean objectionable degree of oxidization of the permalloy tape. For thesakeof clear- Vness this apparatus has been shown schematically butreference is made to' an application of F. S. Kochendorfer, Serial No.601,021, filed November 15, 1922, which has issued as Patent No.1,624.668 on April 12, 1927 and which discloses the preferred form ofapparatus to be used.

With a structure constructed as described danger of embrittling theconductor during the heat treatment is eli1ninated,even though grease,oil or other matter is attached to the conductor as it enters thefurnace and even 'first been reduced.

strain.

It has been determined that a very thin layer of black copper oxide willbe effective in preventing embrittling of the copper.

The coating of copper oxide furthermore prevents the copper conductorfrom alloying with the magnetic tape when the taped conductor issubjected to the high temperatures required for the heat treatment.Therefore, adhesion between the conductor' and tape during the coolingprocess with resulting stresses in the material is prevented and thehigh permeability of the material is main-v tained.

While the use of a layer of metallic oxide between the conductor andloading material has been described as applied to a stranded conductor,its use is of particular importance in preventing adhesion when appliedto a solid conductor.I ln the case of a loaded stranded conductor, thereis a certain amount of looseness in the structure which preventsadhesion and which is not present when the loading tape is wound on asolid conductor. Therefore, inthe latter case there is an even greaternecessity for providing some means for preventing adhesion.

vWhat is claimed is:

1. In a continuously loaded conductor which requires a heat treatment tohigh temperatures to develop one of its magnetic properties, a copperconductor having near its surface a zone of a material containing a fargreater amount of oxygen per unit volume than does the conductor at itscenter.

2. A loaded signaling conductor comprising a central conductor, acoating of redueible material about said copper conductor, and amagnetic loading material forming a wrapping close about the coatedconductor, said loading' material when on said coated con- ILOG ductorrequiring heating to high temperaoxide about said conductor, and amagneticl loading material forming a wrapping close about the coatedconductor, said loading material after being placed on said coatedconductor requiring heating to high temperature to develop highpermeability therein and the permeability of which is sensitive tostrain.

4. A loaded signaling conductor comprising a central copper conductor, acoating of metallic oxide about said conductor, and a magnetic loadingmaterial wrapped closely about the-coated conductor, said loadingmaterial after being placed on said coated conductor requiring heatingto high temperature to develop high permeability therein and thepermeability of which is sensitive to 5, A loadedD signaling conductorcomprising a central conductor, a coating of copper oxide about saiducopper' conductor, and oa magnetic loading materialforming aWrappingclose about the coated conductor, v,said loading material beingin such a state that it requires a heating cand cooling treatment todevelop high permeability therein and the permeability of which issensitive to strain.

6. A loaded signaling conductor comprising `a central copper conductor,a coating of copper oxide about said conductor, and a' magnetic loadingmaterialforming a Wrapping close about the coated conductor, saidloading material comprising a nickel iron alloy consisting ofapproximately TS1/2% nickel and SM1/2% iron and being in such a magneticstate that it requires a heating and a cooling process to improve itspermeability.

7. A method of continuously loading a copper conductor with magneticmaterial which requires a heat treatment to high temperature after itsapplication lto the conductor in accordance With which a supply ofmetallic oxide is placed under the loading material before the.commencement of said heat treatment, said supply being suiiicient tomateriallyreduce :embrittlement of the copper due to the presence ofreducing gases during said heat treatment.

8.V A loaded signaling conductor comprising a central copper conductor,a magnetic lloading material to be heat treated after its application tothe conductor composed largely of nickel and iron and enveloping saidconductor, and a spacer of copper oxide separating said conductor andsaid loading material to prevent interaction therebetween and to preventembrittling of said conductor during a heating process Which may beapplied to said loaded conductor to'improve the permeability of saidloading material.

9. The method of constructing a continuously loaded signaling conductorwhich comprises treating the surface of the conductor" to produce alayer of metallic oxide thereon, placing a layer of loading materialover the metallic oxide and heat treating the loaded conductor.

010. The method of constructing a continuously loaded signalingconductor which comprises treating the surface of the conductor toprovide a layer of copper oxide thereon, placing a layer of loadingmaterial over the copper oxide and heat treating the loaded conductor.

11. lThe method of continuously loading a copper' conductor whichcomprises produc- Yinga surface coating of copper oxide on the conductorduring the annealing process, covering the conductor With a loadingmaterial requiring heat treatment, and heat treating the loadedconductor.

' 12. The method of constructing a continuously loaded copper conductorwhich coin- 26th dayvof December, A. D.

OLIVER E. BUCKLEY.

